Mesa Color Code on Power Tubes

[nevetslab]

I just took in a Mesa Triple Rectifier Solo Head a couple days ago, which was blowing the Mains Fuse. After finding one dead 5U4GB rectifier tube, and found the shorted 6L6GC (Mesa AC10-YEL), I was left with four working Mesa AC10-GRY 6L6GC tubes and an AC10-YEL 6L6GC tube. I broke out the Bias Probe meter, plugged in the two probes into the end tube sockets (vacated during finding the shorted tube at one end), and went thru to see what these remaining tubes' Plate Current read at idle. I found 15mA/6.0W, 18mA/7.2W, 22mA/8.9W and 23mA/9.2W on the four AC10-GRY tubes. The remaining AC10-YEL read 12mA/4.8W.

I looked thru my collection of Mesa 6L6GC tubes, found two boxes of AC10-RED, both which read 4mA, an AC10-GRN which read 3.5mA. I tried a number of other 6L6GC pulls I had on hand, being out of new 6L6GC's here in the shop, not finding anything usable to match what's in the amp. Went and brought the three matched pairs from the Guitar Dept, two pairs read 12mA, and the last pair measured 13mA & 16mA, and settled for those, grouping the 15mA with the 23mA tube, the 18mA with the 22mA tube, then put the new 16mA tube in with the 15mA/23mA tubes and the 13mA tube with the 18mA/22mA tube, yielding 54mA and 53mA total plate current per half.

Does anyone know what the Color Code means in terms of Plate Current in Mesa's Color Code scheme? Granted, here, I'm working with only plate current numbers, and not with other parameters that can be matched with different computer-controlled Power Tube matching systems, given bulk tube quantities of different mfgr's tubes to pull from. I know the customer wouldn't want to have to purchase a matched Sextet of power tubes while having 4 tubes reasonably close to working set, and instead just adding a pair to it.

I thought I had run across an article someplace on their color code relative to plate current, but couldn't find it in my files.

[christarak]

Yes, I believe RED means hit amp with a 10lb mallet and yellow means throw Triple and Dual Rectifiers out of vehicle window at a minimum of 50mph.

[nevetslab]

Yes, I believe RED means hit amp with a 10lb mallet and yellow means throw Triple and Dual Rectifiers out of vehicle window at a minimum of 50mph.

AMEN to that!!! When I got this amp powered up after selecting the replacement power tubes, I started with Ch 1, tone pots centered, Master and Gain down, Output control turned up around 2 o'clock. I turned up the Gain, then while turning up the Master on Ch 1, Switch was in PUSHED mode, the 4 ohm SVT115HL4 woofer began slamming between it's mechanical limits from the built-in 13Hz Oscillation these amps have designed into them!!! Quickly turned the Output control down. Bloody amps can quickly kill your guitar cabinets with that sort of thing!!!

[Pedro Vecino]

From my experience yellow tends to correspond to low quiescent plate currents relative to higher gray and blue. I think the green ones are in the middle of those two groups. However, it is common to find overlaps between two and even three consecutive colors.
All this within the same 6L6 model (STR xxx).

[drewl]

Maybe call them and ask?

Maybe we can post our findings and figure it out ourselves
To me Mesa's = $$$$$$

[J M Fahey]

They won´t answer beyond "Buy the recommended parts from us or a Distributor"

On one side they do provide a Service to customer by avoiding a "Bias Job", on the other they keep customers captive.

We should open a thread where Forum Members measure fresh out of the box Mesa tubes and post results there.
After a while, a pattern will become clear.

That, if colours or letters are not assigned by rolling dice or throwing darts at a coloured band target

Serious, it should be a stickie.

4 parameters should be shown: current - bias voltage - plate voltage - screen voltage, for a full picture.

Eventually we will be able to "Mesa rate" any brand tube bought anywhere else.

[Chuck H]

If people start chiming in with Juan's requested figures I'll sticky the thread.

Any amp with Mesa tubes can be tested. Not just Mesa amps.

[nevetslab]

They won´t answer beyond "Buy the recommended parts from us or a Distributor"

On one side they do provide a Service to customer by avoiding a "Bias Job", on the other they keep customers captive.

We should open a thread where Forum Members measure fresh out of the box Mesa tubes and post results there.
After a while, a pattern will become clear.

That, if colours or letters are not assigned by rolling dice or throwing darts at a coloured band target

Serious, it should be a stickie.

4 parameters should be shown: current - bias voltage - plate voltage - screen voltage, for a full picture.

Eventually we will be able to "Mesa rate" any brand tube bought anywhere else.

Hey, I like that thought!! Mesa does have a discussion article on their website, or at least I found it while searching for clues, and it briefly discussed their computer-assisted grading systems that end up getting color branded. I'll have to find that link and post it to this thread.

Thanks for the suggestoin, Juan!